Cylindrical current sense resistor

ABSTRACT

A resistor includes a substantially cylindrical resistive element having a resistance of less than about 1 mΩ, a substantially cylindrical first termination electrically connected to the resistive element and a second termination electrically connected to the resistive element. The substantially cylindrical first termination is hollow to allow for accepting a connection such as from a battery cable. In addition there may be sense leads present on the resistor. A method of forming a substantially cylindrical resistor includes forming a hollow cylindrical resistor body by rolling a flat sheet comprising a resistive element and a first termination and a second termination joined on opposite ends of the resistive element.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No. 12/026,939, filed Feb. 6, 2008, now U.S. Pat. No. 7,911,319, issued Mar. 22, 2011, which is incorporated by reference as if fully set forth.

FIELD OF INVENTION

The present invention relates to resistors, particularly resistors in automotive and related applications.

BACKGROUND

As electronics content in a typical vehicle has substantially increased, the demands on the battery and charging system of a typical vehicle have also increased. Moreover, with the advent of the hybrid gas-electric car and all-electric cars the battery and charging system becomes an evermore vital part of a vehicle. An unhealthy electrical system in today's car can jeopardize vital functions such as steering and braking.

Therefore, it has become essential for onboard computers to have sensory information about the charge used, charge returned and charge available from the battery and the overall health of the charging system. The main sensor for this is a current sense resistor integrated into the battery cable.

Traditionally, this is a flat resistor made of a MANGANIN resistive element terminated by copper pieces welded or brazed to each end of the resistive element. MANGANIN is an alloy typically 86 percent copper, 12 percent manganese, and 2 percent nickel which provides low resistance. This flat resistor would be located at the end of the cable adjacent to the connector to the battery and would be surrounded by support electronics encased in a potted container. Such a resistor may also be used in applications other than automotive application such as, but not limited to, galvanic plating power supply cables, welding cables, and other applications.

Therefore, it is a primary object, feature, or advantage of the present invention to improve over the state of the art.

It is a further object, feature, or advantage of the present invention to provide a resistor suitable for use in automotive and related applications where the resistor is connected to a cable.

Yet another object, feature, or advantage of the present invention is to provide a resistor which allows current sensing.

One or more of these and/or other objects, features, and advantages of the present invention will become apparent from the specification and claims that follow.

SUMMARY

According to one aspect of the present invention, a resistor includes a substantially cylindrical resistive element having a resistance of less than about 1 mΩ, a substantially cylindrical first termination electrically connected to the resistive element, and a second termination electrically connected to the resistive element. The substantially cylindrical first termination is hollow to allow for accepting a connection such as from a battery cable. There may be one or more sense leads attached to the resistor.

According to another aspect of the invention, a method of forming a substantially cylindrical resistor is provided. The method includes forming a hollow cylindrical resistor body by rolling a flat sheet comprising a resistive element and a first termination and a second termination joined on opposite ends of the resistive element.

According to another aspect of the invention, a method of forming a substantially cylindrical resistor includes providing a first tube for a first termination, providing a second tube for a second termination, and magnetic pulse welding a resistive element between the first tube and the second tube to thereby provide a substantially cylindrical resistor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of one embodiment of a cylindrical resistor of the present invention.

FIG. 2 is an exploded perspective view of one embodiment of the cylindrical resistor of the present invention.

FIG. 3 is a perspective view of the cylindrical resistor connected to a battery cable assembly of a vehicle.

FIG. 4 is a perspective view of the cylindrical resistor connected to a battery cable of a vehicle.

FIG. 5 illustrates a step in the process of forming a cylindrical resistor according to one embodiment.

FIG. 6 illustrates a step in the process of forming a cylindrical resistor according to one embodiment.

FIG. 7 illustrates a step in the process of making a cylindrical resistor according to one embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is generally directed towards a cylindrical resistor and a method of making the cylindrical resistor. The cylindrical resistor may be used in applications such as, but not limited to, automotive applications, galvanic plating power supply cables, welding cables, and other applications. The cylindrical shape allows the resistor to be integrated into a cable assembly in a more space efficient manner and also allows insertion at any position along the length of the cable. Flexibility in positioning allows support electronics to also be positioned in a location closer to other electronics modules or at the battery terminal.

FIG. 1 illustrates a perspective view of one embodiment of a cylindrical resistor 10. The cylindrical resistor 10 includes a resistive element 12. The resistive element 12 may be made from a cylindrical piece of Manganin wire, or other suitable resistive material. Each end of the resistive material is terminated with copper or another suitable conductive material to form the terminals 14, 16 of the resistor 10. The terminals 14, 16 may be used to connect the resistor 10 to the cable assembly and carry the main current. These terminals 14, 16 are attached to resistive element 12 by welding, brazing or crimping. The terminals 14, 16 may be capable of attachment to a battery cable assembly by welding, brazing or crimping. The geometry of the terminals may vary based on the particular application for which the cylindrical resistor is used and the present invention is not to be limited by the specific geometry of the terminals shown.

Integral to the attachment of these terminations there are one or more sense leads 22, 24 attached to the terminals 14, 16. These sense leads 22, 24 are used for connection to support electronics that require a sense voltage input in proportion to the electrical current passing through the resistor 10. These leads 22, 24 may be an extension of the resistor terminal material or may be otherwise added such as through welding, brazing, crimping, or other means. The specific geometry of these sense leads may vary according to specific applications and environments and the present invention is not to be limited to the specific geometries shown.

In one embodiment, the assembly of this shunt resistor 10 consists of copper tubes for the terminations 14, 16 and a piece of a substantially cylindrical MANGANIN resistance wire as the resistive element 12. The resistance wire is cut to a short segment. One end of the segment of resistance wire is placed in the end of one copper tube and the two are joined by a magnetic pulse weld that uniformly collapses the tube onto the wire at such speed that a weld occurs. The other end of the Manganin wire resistive element is inserted into the end of the other copper tube and joined by another magnetic pulse. Thus, a resistor such as resistor 10 in FIG. 1 is formed.

The amount of unwelded resistive material between the ends of the two copper tubes determines the blank resistance value. Adjustment of the resistance value can be made by a lathe, abrasion, or lasering operation that reduces the diameter of the exposed MANAGANIN wire or by removing copper from the end of each tube effectively lengthening the MANGANIN resistive element. In addition, resistance can be adjusted by adding termination material (such as copper or other conductive material) back to the resistive element such as by welding. At this point the open ends of the copper tubes are ready to accept further processing steps to connect them to a cable assembly. Such as inserting cable 34 into the open tube and magnetically pulse welding the two pieces together as shown in FIG. 4. This joint could also be made by soldering, crimping, brazing or other welding methods. A battery post clamp 30 having an end 32 could also be inserted to one of the open tube ends and secured in place as shown in FIG. 3. The battery post clamp may be secured by soldering, crimping, brazing, or other welding methods.

FIG. 5 and FIG. 6 illustrate another embodiment of a cylindrical resistor. In this embodiment, the resistor utilizes a flat resistive element of Manganin, or other suitable resistive material, with copper, or other suitable conductive material, terminals welded to each end of the resistive material in the same fashion as may be used in fabricating power metal strip resistors such as disclosed in U.S. Pat. No. 5,604,477 to Rainer, herein incorporated by reference in its entirety.

In FIG. 5, a flat sheet 39 is shown. The flat sheet 39 includes a resistive material 42, and terminal material 40. The terminal material includes a first portion 40A and a second portion 40B on opposite sides of the resistive material 42. Sense lead 22 is electrically connected to and extends from the first portion 40A of the terminal material 40 while sense lead 24 is electrically connected to and extends from the second portion 40B of the terminal material 40.

The flat sheet 39 is rolled into a cylinder with the resistive material 42 becoming a band that curves around the circumference of the cylinder as best shown in FIG. 6. The resistive material 42 and terminal material 40 may have holes or slots 46 in specified areas to facilitate the roll forming process and to facilitate crimping to a cable. These slots 46 may also be used to adjust resistance value and TCR. The material from these slots 46 may be separated from the main body on three sides yet left connected on the fourth side to form a sense terminal integral to the resistor material.

In another embodiment, shown in FIG. 7, the resistor is configured to allow for one termination 40A to be cylindrical for attachment to a cable while the second termination area 40B has a flat terminal 48 which may include an aperture 50. The flat terminal 48 may be connected to a battery post or other stud mount connector.

Note that when the cylindrical resistor is hollow, the resistive element may be cooled by circulating a fluid through it. Cooling may be desirable in certain environments.

The cylindrical resistors of the present invention have resistance values less than 1 mΩ and are designed to handle current of 200 A or more. Thus, the cylindrical resistors are well-suited to automotive applications, battery monitoring applications, and related applications where a low resistance is desired.

Therefore, a cylindrical resistor has been disclosed. The present invention contemplates variations in the size, shape, materials used, resistance, and other variations. Although various embodiments are shown and described, the present invention is not to be limited to the specific embodiments shown. 

1. A method of forming a substantially cylindrical resistor, comprising: providing a first tube for a first termination; providing a second tube for a second termination; magnetic pulse welding a resistive element between the first tube and the second tube to thereby provide a substantially cylindrical resistor.
 2. The method of claim 1 further comprising determining a distance between first and second tubes to set an initial resistance value, positioning the first and second two tubes on the resistive element at the distance and magnetic pulse welding a resistive element to the first and second tubes.
 3. The method of claim 1 further comprising connecting a first sense lead to the first tube and connecting a second sense lead to the second tube.
 4. The method of claim 1 further comprising removing a portion of the resistive element material to increase resistance.
 5. The method of claim 1 further comprising attaching conductive material to the resistive element to decrease resistance.
 6. The method of claim 1 further comprising providing substantially cylindrical resistance wire as the resistive element.
 7. The method of claim 1 further comprising positioning the resistive element in the first and second tubes leaving first and second open ends in the first and second tubes respectively.
 8. The method of claim 1 further comprising securing a cable in the first open end.
 9. The method of claim 8 further comprising magnetic pulse welding a cable in the first open end.
 10. The method of claim 1 further comprising forming a flat terminal area in the second termination.
 11. The method of claim 10 further comprising forming an aperture in the flat terminal area.
 12. The method of claim 1 further comprising forming at least one slot in the first or second termination to facilitate crimping to a cable.
 13. The method of claim 1 wherein the resistive element has a resistance of less than 1 mΩ. 